As drive power sources of mobile electronic apparatuses, such as a mobile phone including a smart phone, a mobile computer, a PDA, and a mobile music player, many nonaqueous electrolyte secondary batteries represented by a lithium ion battery have been widely used. Furthermore, many nonaqueous electrolyte secondary batteries have started to be used as power sources of electric vehicles (EV) and hybrid electric vehicles (HEV and PHEV) and also in stationary storage battery systems used, for example, for application to reduce the variation in output of solar energy generation, wind energy generation, and the like, and peak-shift application of system power control in which an electric power is stored during nighttime and is consumed during daytime.
In particular, since having various battery characteristics superior to those of other materials, a lithium cobalt composite oxide (LiCoO2) and a foreign element-added lithium cobalt composite oxide in which Al, Mg, Ti, Zr, and/or the like is added have been widely used. However, cobalt is an expensive element, and in addition, the abundance thereof as the natural resource is very limited. Hence, in order to continuously use those lithium cobalt composite oxide and foreign element-added lithium cobalt composite oxide as a positive electrode active material of a nonaqueous electrolyte secondary battery, further improvement in performance thereof has been strongly desired.
As one method for improving the performance of a nonaqueous electrolyte secondary battery using a lithium cobalt composite oxide and/or a foreign element-added lithium cobalt composite oxide, there may be mentioned a method in which the charge voltage is increased from 4.3 V, which is a generally used potential, to approximately 4.6 V (each of which is a potential with reference to lithium). On the other hand, by the increase in charge voltage, problems in battery characteristics may occur in some cases, and hence, the measures therefor are required.
Patent Document 1 has disclosed a nonaqueous electrolyte secondary battery in which when the battery is charged for use so that a positive electrode potential exceeds 4.3 V with reference to lithium, in order to suppress elution of cobalt and decomposition of an electrolyte liquid, a positive electrode is used which includes lithium phosphate and a positive electrode active material containing a lithium cobaltate to which at least one type of Mg, Al, Ti, and Zr is added.
Patent Document 2 has disclosed a nonaqueous electrolyte secondary battery in which when the charge voltage is increased, in order to suppress a reaction between a nonaqueous electrolyte liquid and a positive electrode active material by improvement thereof, a positive electrode active material is used which includes positive electrode active material grains each containing lithium and grains of a compound, such as erbium hydroxide or erbium oxyhydroxide, adhered in a dispersed state to the surfaces of the above active material grains.
In order to obtain a battery having a high capacity, excellent continuous charge storage characteristics, and excellent cycle characteristics, Patent Document 3 has disclosed a nonaqueous electrolyte secondary battery configured to comprise a positive electrode active material which includes a lithium transition metal composite oxide containing lithium and cobalt and having a layered structure and fine grains of at least one of a hydroxide and an oxyhydroxide of a rare earth element adhered to the surface of the composite oxide; a positive electrode active material which includes a lithium transition metal composite oxide containing lithium and cobalt and having a layered structure and no fine grains of a rare earth element compound adhered to the surface of the composite oxide; and lithium phosphate.